I have recently encountered a problem with my computer that took me over a month of investigation to figure out. I first noticed it when I upgraded my old single core AMD to an Intel quad core system. When trying to play Starcraft 2 on the newer system, the game would run at half speed; units were slow in general, and the clock in timed missions were taking 2.5 seconds to count off 1 second. I originally thought that I had fixed the problem by changing display settings to max performance. I recently picked up SWTOR, and had no problems running it at first. After a recent Windows update, the problem came back and was affecting SWOR as well.
After checking all my settings, I noticed that the update had reset my power and display settings to default, so I changed them again but this time the problem remained. That's when I started noticing that the entire system seemed to be acting in slow motion, not just the afore mentioned games. After checking with Microsoft answers and following their cookie-cutter support advice, I came across a thread on an obscure forum about someone having a similar problem, only to discover that a USB mouse was the root cause. So, I unplugged all of my USB devices and re-booted. Lo and behold, Windows was lightning fast again, and the games are now running normally. I have ruled out my mouse as the culprit, and am suspecting a SD card reader I had plugged in as the cause.
How can a simple card reader cause the entire OS to slow down like this?
Note: the slow down never affected oled games like Diablo 2.
When a USB device gets into the weeds or a new device is connected, the USB controller driver will issue a port reset. Depending on the HCI of the port (EHCI, UHCI, OHCI, or XHCI) sometimes the port reset will have to spin on a port control register (other types are interrupt-driven) until the reset complete bit is set (or the reset bit is clear). This spinning causes the USB driver to use up more significantly CPU time than it normal would. It's not usually noticeable, but if the resets cascade, it may start to cause problems. If the SD controller is acting out of spec or something, that can cause the USB mass storage driver to issue a port reset. If the behavior repeats, a loop of resets would result.
This problem with slow boot due to misplaced USB device can get REALLY NASTY on some machines, like my HP Pavilion Elite HPE (which I really love):
If you accidentally leave a USB flash-chip plugged into the upper-leftmost port on the Pavilion's front panel (or whatever is the primary USB port on your machine), the computer will attempt to boot from that device rather than the hard disk. Chances are that your USB device is not actually a boot device, and so the boot will abort with a cryptic "Cannot find boot device" message.
This is a traditional annoyance we've seen for years on Windows machines: All you needed to do was pull out the device and then recycle the power switch to get the correct reboot.
BUT NOW IT'S TOXIC:
The aborted boot process somehow maims the bus environment around the AMD Radeon Graphics Controller. From now on, crucial vector graphics operations will be detoured into software emulation, causing most "cool" visual effects to crawl at half speed, including the dancing lights in all Windows7 boot-ups, including the animation of windows maximizing and minimizing, games, Flash animations, etc.
If you navigate to HP Support Assistant >> Troubleshoot >> Graphics, Video and Display, you can run a diagnostic on your AMD Radeon chip and it will FAIL. (Oddly enough, the diagnostics available through the Windows7 Control Panel Devices manager all seem to say the chip is healthy). Incredibly, you cannot fix this problem by downloading a fresh copy of the chip's driver software and reloading it into the chip.
THE ONLY SOLUTION I have found is to completely reset the machine back to its factory state. This entails about 45 minutes, and it will delete ALL files and software you have installed. (One way to do this is through Control Panel's "Recovery" feature: Click on the little "Advanced Recovery Options" link and choose to reset back to factory condition.)
The bottom line: NEVER, EVER, plug a USB storage device into your computer's primary USB port: You might forget to remove it if your machine restarts.